RF Systems DX-1
Pro Active Antenna
by John
Plimmer
The first question to ask
is why choose an active antenna over a good wire
antenna? I have successfully used wire antennas
all of my DXing life - that was for 30 years until
I retired to this little town of Montagu in South
Africa. Here I tried every combination of wire antenna
with dismal results. I put this lack of success
down to the rocky and stony ground and the fact
that the area has a power supply of overhead street
lines, plus a high voltage powerline in front of
the house.
I then bought a K9AY from
Wellbrook, which, after careful installation and
much e-mail between me and Wellbrook turned out
to be a dismal failure. Andy Ikin of Wellbrook very
kindly took it back and gave me a full refund. Now
I had no antenna at all except an old Datong AD270
active antenna, which at least allowed me some reception.
So
I searched around for a better more uptodate active
antenna and was impressed with the review of the
RF Systems DX-1 Pro in the 1996 WRTH. I then enquired
around on the web for user comments and finally
Michael Schnitzer gave me a comprehensive and detailed
review of the DX-1 Pro that encouraged me to buy
one direct from Holland.
It arrived and was installed in October 2000. From
other users comments and carefully following RF
Systems instructions, I installed the DX-1 Pro on
a 5 meter pole mounted on an outbuilding. This was
high enough to ensure the head unit was at least
one meter higher than the offending powerline that
had blocked reception of the wire antennas.
Grounding
is important
Grounding
was said to be particularly important, so I paid
a lot of attention to that. The careful grounding
ensures both a "ground" plane to the antenna
and has a lot to do with diminishing the effects
of local man made QRM. It also bleeds off and grounds
the static that would otherwise damage any active
antenna, something that is a real danger in the
hot dry high winds experienced in this semi-desert
area.
Before
choosing the final position of the head unit, I
had an assistant walk around with my lightweight
Datong active on a pole, thus allowing me to carefully
choose the position with the least noise generated
by my household and the neighbours noisy TV's and
satellite dishes.
Thus, the "head" unit ended up some 30
meters away from the indoor control unit at the
radio in the shack. To minimise loss and ensure
the least QRM pickup, RG213 cabling was used. Two
"grounds" were provided, one at the head
unit into a heavy copper cable at it's base, and
another at the indoor control unit. These have proved
very effective as the unit has not suffered from
static damage in the strong dry winds and reception
has been superb.
The head unit may be described as having an "egg
beater" configuration and is 1.25 H x 1.1 W
meters. It has a very robust connection to the supporting
pole and has withstood four years of high winds
and lashing rain, some winds gusting up to 100 km/h.
The indoor control unit is of modest size and has
only two controls - an on/off MW suppression of
55 dB and a rotary attenuator control. This control
allows attenuation of up to minus -40 dB in 10 dB
steps and also +6 dB of boost. There is a LED to
indicate power is on to the unit, but no on/off
mains switch, as RF Systems state that it is built
to "milspec" and is designed to be left
"on" continuously. Two SO 239 outlets
for two receivers are provided.
Quiet and sensitive
The
antenna is extremely quiet and seems to offer a
lot of suppression to local man made RF noise, whilst
at the same time being very sensitive. Sensitive
and quiet enough to get those very faint DX signals
from the corners of the globe. In practise I have
never found it necessary to use the +6 dB of boost
available.
I must point out that my QTH of the little town
of Montagu is far from being an ideal DX location,
as it is at an altitude of 230 meters but surrounded
by the 1400 meter high peaks of the Langeberg mountain
range which tend to block out the incoming low angle
DX from far distant stations. But when rare openings
do occur, the DX-1 Pro has achieved results comparable
with my seaside DXpeditions using 300 meter long
beveridges.
Some catches obtained on the DX-1 Pro:
198 kHz, BBC Droitwich, UK, 9,800 km's distant
1410 kHz, WKKP, Mcdonough GA, USA, 13,190 Km's distant
- only 58 watt TX output
1700 kHz, KVNS, Brownsville TX, USA, 14,040 Km's
distant - 880 watt TX power
4 MHz Tropical Band, RRI Fak Fak and Serui, 1 Kw
TX power 12,300 Km's distant
10,320 kHz, AFN Pearl Harbour, 3 Kw TX power 18,640
Km's distant.
28,266.3 kHz, Pirttikoski Finland, 20 watt TX power
11,000 Km's distant
(the DX-1 Pro is fed to a Drake R8B receiver)
I must stress that the above reception is only possible
on an antenna that is both very sensitive and extremely
quiet, which is the DX-1 Pro's characteristics.
I can only wonder at what reception I would receive
on this antenna if I was in a more ideal DX location.
Visitors to my QTH remark on how quiet the system
is and what a superb signal to noise ratio it has.
The frequency coverage of the DX-1 Pro is from 20
Khz to 54 Mhz. It has an outstanding third order
intercept point of +50 dBm and I have never heard
of anybody reporting intermod or spurious signals
on it. The receiving pattern is omnidirectional.
So for four years I have experienced superb reception
of the faintest stations from the furthermost parts
of the globe on this outstanding antenna and would
highly recommend it to any aspirant DXer. The caveat
is that it must be installed exactly as per RF Systems
instructions - that is high up and above the nearby
roofs and trees, and properly and well grounded.
As to the reliability,
affter two years the rotary attenuator switch packed
up. RF systems sent a replacement no charge that
I replaced locally. After four years a simple $1
component packed up in the indoor control unit,
probably due to the very high desert area heat here
in Montagu. RF Systems would not supply the wiring
diagram schematics to repair this locally, but instead
sent a complete PCB board replacement, again at
no charge.
Expensive,
but worth the money
Passport to
World Band Radio says in it's review of this antenna
"it's unbalanced design makes it prone to pick
up local electrical noise". On the contrary,
in my noisy suburban location I find that in fact
it suppresses this to a great extent. This is very
apparent when I compare it with my Datong AD 270
active antenna that is extremely noisy by comparison.
According to the review the DX-1 Pro is very expensive
and not worth the money. I don't agree that it is
not worth the money. If I want a fine cigar I will
pay the extra for a Cuban, if I want a fine brandy
I will pay the extra for a superb French Cognac.
The DX-1 Pro, whilst expensive, is the best active
antenna for the money and will yield superlative
results.
You will be better off with a Wellbrook ALA 330
or ALA 1530. To get the same results as the DX-1
Pro you are going to have to mount it on a rotator,
as the Wellbrooks are directional antenna's. This
is going to make it equal in cost to the DX-1. Also,
from various reports, the DX-1 is far more robust
for outside mounting. I have not seen reported results
of Wellbrook antenna's exceeding the results I obtain
on the DX-1 Pro.
The DX-1 Pro is now replaced by the DX-1 Pro MkII.
My DX-1 Pro was supplied by Deltron
Trading BV, the Netherlands.
published on February
3, 2005
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